Exponential Growth #4: Containment (May 23)

In past posts I’ve talked about exponential growth when it’s fast and scary, and when it’s close to flat. But there’s also negative growth, with a multiplier of less than 1.

Right now, the Rt Tracker website shows all but four states with Rt like that, from Arkansas (.99) all the way down to Alaska (.63). If they can stay below 1 for long enough, Covid-19 eventually will reach containment.

Here is a chart of exponential growth rates less than one. It shows how the number of new cases of Covid-19 will decrease for each Rt multiplier. The lower the number, the faster the approach to zero.

Right now there are four states with Rt values under .82: Alaska, Hawaii, Vermont, and Montana. All have relatively small, isolated populations. They never had many cases to begin with, and are close to zero now. With local containment achieved, their biggest worry is new cases that come in from elsewhere.

The next lowest state is Connecticut, with an .83 multiplier. They had over 2000 new infections at the daily peak, but the average is about 600 now. At current rate of decline, it will take roughly 50 days to drop by a factor of 10 (to 60 new cases per day). Another 50 days gets it to 6 new cases. The theoretical curve never reaches zero, but with actual humans it’s possible to get there eventually.

Other states with higher Rt values will decline more slowly. Some will be very, very slow.

Exponential curves and Rt charts are pretty, but they are just theory. Actual containment depends on what people do each day: how much they stay home, how much they congregate, whether they wear masks. Just as important is the work of state and local health departments. They have battled all sorts of diseases over the past century, and this is just another for them.

To contain a disease, health departments do whatever it takes to reduce the infection growth rate to something less than one, then keep it that way.

Vaccines are the best way to contain a disease. Many folks are working on them for Covid-19. Next best is contact-tracing and quarantines. If those aren’t enough, then the only recourse left is massive social distancing. Economically, it’s an extremely painful option, but less bad than having many people suddenly sick and dying at the same time.

The ideal way to conquer a dread disease is to get global containment: already accomplished for smallpox, and almost completed for polio. Total containment is very hard work. Health workers must go into poor and war-torn regions and vaccinate enough people to reach “herd immunity”. It also requires plenty of contact-tracking and isolation until the last cases are completely gone. One sad consequence of Covid-19 is that it sets back the efforts to eradicate polio.

The Rt tracker site seems like a very useful tool. However, Rt is based on actual test results. It lags by at least a couple weeks, because it takes time for infections to develop, tests to be processed, and data to be entered into the pipeline. Today’s numbers reflect conditions from when state just started to reopen in early May. The social distance scorecard is probably the best way to predict the future, but it’s a very crude guide based on smart phone locations. It doesn’t adjust for mask use, indoor vs outdoor contact, or sanitation measures. Lately it rates most of the US at D or F, but I think reality is a grade or so better.

As social distancing relaxes, it will be interesting to see how much it affects the numbers. States will probably jump around with changes in weather, policies and people’s behavior. The risk is always there for an outbreak, with a sudden return to scary exponential growth. A single ‘super-spreader’ event can push any state to well above 1.

SARS and MERS were caught soon enough to be 100% contained. Covid-19 became too global, and it’s unlikely to ever reach full containment. Even with a vaccine. However, it can become like measles, influenza and other diseases that are controlled enough to not cause big catastrophes.

Dennis Kolva
Programming Director
TurtleSoft.com

Covid-19 and Construction #4 (May 16)

Two months ago, I first blogged about Covid-19. Since then, much has changed. Way more than I expected back then.

OpenTable has a spreadsheet for restaurant visits in 36 states, plus a few other countries. Here is their US data in chart form:

It only took two weeks to drop from normal (Mar 8) to zero (Mar 22). Many Governors shut down their states during that period, but the public was usually ahead of them by a few days. The collapse was close to simultaneous across the whole US, and also in Canada and most of Europe. Reopening started a couple weeks ago in a few states and countries, but it’s still very sparse.

What will Covid-19 do as social distancing relaxes? It may fade out for the summer as flu does. Maybe contact-tracing and moderate distancing will be enough to keep it controlled. Maybe there will be exponential outbreaks. Most people are taking it slow, which helps. Those who rush off to crowded bars and church services will be our guinea pigs.

Meanwhile, most of what I said back in March still makes sense. Here’s a slightly revised recap of my advice for construction companies:

  • Stagger work hours & locations. The less time people spend close to each other, the slower disease spreads.
  • Be clear with employees and subs. Send them home ASAP if sick, or don’t even let them come in. This might be time to start paying sick leave. Emphasize the need for testing and self-quarantine. Get a non-contact thermometer, and check people for fever.
  • Be clear with clients. If you work in client homes, let them know your plans. You might need to add plastic sheeting barriers, and sanitize more thoroughly at day’s end. Switch to outdoor work, if possible.
  • Take the usual precautions. Wash hands often. Sanitize surfaces that are touched frequently. Cancel group events. Practice social distancing. Listen to local & state health departments. Most are developing reopening guidelines now. The rules probably will be tweaked as time goes by.
  • Wear face masks. Back in March, CDC said not to use masks. Fortunately, their guidance has changed. I think masks may be the #1 way to stay safe, and still run a business. It’s worth elaborating.

Why wear face masks?

Covid-19 spreads mostly by respiratory droplets, which come in a wide range of sizes. Coughing and sneezing produce tons of them. Talking creates plenty. Even normal breathing makes some. The bigger droplets blow out a few feet, then drop quickly. They coat everything with virus gunk- that’s why it’s important to wash hands, and not touch your face.

The smaller droplets (aerosols) linger in the air. They can travel 20+ feet on air currents. Inhale, and they go straight into your airways and lungs. There is debate about how important aerosols are for Covid-19 transmission, but evidence is pretty good that they do cause many infections. Indoor spaces are more risky, especially when people are together there for hours. Air circulation (air changes per hour) makes a big difference.

Snot/saliva/ejected droplets from an infected person will have between 6 million and 2 billion viruses per cc (1 cc = 1/5 teaspoon). Fortunately, the droplets are very small, so only some contain a virus. Unfortunately, there are lots of them. Speaking produces 1,000 to 10,000 small droplets per second. Each cough makes a few thousand mostly bigger ones. Sneezes can make 40K, some of them huge.

Whether a droplet infects you is a matter of chance. Even if you inhale or ingest a virus, many of them get trapped in mucus and never reach a cell. Eventually they exit inside a booger. Others are killed by your body’s innate immune system, which has many anti-viral tricks. It takes a reasonable number of incomings, for even one to infect a cell.

Face masks work in both directions, to prevent that. Outbound, they catch virus droplets that infected people emit into the air and onto surfaces. They make other people safer. Inbound, an N95 removes 95% of aerosols, and almost all larger droplets. Surgical masks are less effective for inbound protection, but still pretty good. Even a bandana is better than nothing.

If everyone is masked, very little gets past the two different filters: one on the cougher, and one on the coughee. The risk of infection goes way, way down. Masks also reduce the odds of getting a really bad infection. I didn’t find any specific data for the effect of initial doses for Covid-19. However, almost all diseases are more deadly if you start with a lot of virus, rather than just a little.

It’s a matter of exponential growth. Once a virus invades a human cell, it starts producing duplicates. Those infect other cells, and it snowballs. The virus count zooms up inside you on a scary steep curve, just like it did globally in March.

Your adaptive immune system has many great ways to kill pathogens, but it takes time to ramp it up. If you started with one virus-infected cell, your defences probably can defeat the infection before it gets too big. You may not even notice any symptoms. Start with a few thousand, and you’ll be very sick. Start with a million or a billion, and you’ll probably die. That’s why Covid-19 kills young, healthy medical workers, especially when they don’t have proper PPE. They absorb a massive dose, the virus starts off strong, and it beats their immune response.

With masks all around, good sanitizing and careful air circulation, you probably can run safe construction projects. At least til Fall.

Dennis Kolva
Programming Director
TurtleSoft.com

The New Normal (May 10)

Some states are starting to reopen, and many residents are eager to get back to the old normal. It shows up in the data: half the states now rate an F on the social distancing scorecard, and only 5 beat a D+. In a month or two, we’ll find out if relaxing was a mistake.

On a personal level, here’s an informative guide to avoiding infection in a reopened world. There’s a lot to be said for not catching Covid-19. It may lose you some work time due to sickness or quarantine. You may die from it, or survive with reduced lung capacity and/or blood clot damage. Or, maybe you infect someone you care about.

On a larger scale, what happens next is hard to see. There are plenty of better experts out there, but here are some guesses on what the new normal will be like.

  • Covid-19 is here for the long haul. It escaped containment and is almost everywhere. Even if some regions stamp it out, someone without symptoms can bring it back in. The disease may reach “herd immunity” eventually, but that will take a few years.
  • Covid-19 may be permanent. Immunity to the 4 species of Coronavirus that cause common colds only lasts a year or two, so they keep circulating. Odds are good that Covid-19 becomes #5. If so, it gradually will become less lethal in the really long haul (decades to centuries). Until then, it will need a vaccine. Maybe an annual one, similar to influenza.
  • Developing a vaccine won’t be quick or easy. Trials have already started, but it takes time to ensure a new treatment is both safe and effective. Previous vaccines developed for Coronavirus diseases in pigs, chickens and dogs had problems. The stakes are higher for humans. After that, ramping production into the 100 millions will also be challenging. 18 months seems the best guess, give or take a few.
  • More testing is needed. Most tests done so far check for viral RNA in the deep part of your nose: it tells if you currently are infected. Simpler saliva tests are in the works. What’s also needed is antibody testing, to see who was previously infected. That includes folks who didn’t show any symptoms. Knowing the overall infection rate helps for planning, and helps catch outbreaks before they become deadly.
  • Still need some social distancing. Large group events of any kind will be risky until there’s a vaccine. People may need to wear masks routinely. The current social distancing measures pushed the R value below 1, but it needs to stay there for a long time. Hopefully there’s a sweet spot so life can go on without killing health workers or grandma.
  • Still need contact-tracing and quarantines. As long as the virus is still circulating, there’s always the risk it grows out of control. State and local health departments have dealt with a few dozen infectious diseases over the past century, and this will be one more that needs attention.
  • The economy will be weird for years. Money is just an arbitrary concept, so in theory we should be able to cancel a few months and get everyone squared up. In practice, nobody has any idea how to actually do that. This new recession isn’t like previous ones. There’s a lot to unravel.
  • The economy will never be the same.  Priorities will change. It’s hard to guess what 2022 will be like, but it won’t be 2019.
  • More Covids are coming. This is the third Coronavirus outbreak since 2003. It’s unlikely to be the last. The next one may spread faster or slower. It may be more lethal, or less.
  • Other pandemics are coming. Influenza sometimes gets deadly. There are always wildcard viruses like Ebola and Zika. Maybe something brand new. Humans are overpopulated and crowded. Nature tends to fix that with diseases.
  • It would help to be more ready. CDC and FEMA kinda dropped the ball, as did many others. We need better prep on all levels: personal, business, county, state, national, global. Fortunately, I think Covid-19 was bad enough to be a wake-up call for most people.

Dennis Kolva
Programming Director
TurtleSoft.com

Covid-19 in New York #2 (May 1)

A couple weeks ago I reported on the impact of Covid-19 on a few mostly-rural counties in upstate NY. Here’s a quick update.

Tompkins County (home of Ithaca, Cornell and TurtleSoft) is still doing well. 132 confirmed cases so far (1oo recovered, 32 active). Still 0 local deaths. The social distancing score has dropped from B+ to C+. However, most people wear masks outdoors now, and masks are required inside stores. That isn’t visible in cell phone location data, but probably makes a big difference.

Tioga County (former home of TurtleSoft) has gotten much worse. In the past week they went from 0 to 14 deaths: mostly in a single nursing home. 98 confirmed cases in a population half that of Tompkins. Social distancing rated a D. I went down there last weekend and nobody wore masks, despite state regulations. Going into the Mini-Mart to pick up a gas receipt felt like a trip back to February.

Steuben County (2 to the west) had it rough in the previous report, and it’s even worse there now. 231 confirmed cases, and 37 deaths in a population similar to Tompkins. Still D for social distancing.

New York State has started small-scale antibody testing (which shows past infection, even if no symptoms). Results are very preliminary, but they suggest that 20% to 25% of folks in New York City may have been infected already. In NYC suburbs it ran 10%, and only 2.5% around here. “Herd immunity” probably requires at least 60% infected, so everyone still has a ways to go.

The theme locally (and elsewhere) is that even rural areas have places that are crowded. Infections can run rampant there. Nursing homes are the most likely target, but prisons, meat processing plants and factories are also hot spots.

It’s a systemic problem, since employees that work in all those places are often poorly paid, often with no benefits. They probably live in more crowded housing that is prime for transmission. And of course, the high cost of healthcare in the US means they are less likely to call in sick, or get treated.

I have no idea how any of this will correlate with conditions in the rest of the US. Too many unknowns.

Dennis Kolva
Programming Director
TurtleSoft.com